More than 400,000 customers in the Northeast are without power due to severe weather that will include thunderstorms, flash flooding, hail, winds up to 80 mph and possibly tornadoes.

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As of 5:40 p.m. ET, shortly after the storm began, 408,158 customers in Pennsylvania, New York, New Jersey and Connecticut had lost electricity.

Service on one of the busiest train lines in the Northeast has been suspended due to the weather.

All of the Metro North lines have been suspended due to downed trees, leading to a frenzy at Grand Central Station in New York City during rush hour on Tuesday. Thousands of people were stranded at the station, ABC New York station WABC reported.

Amtrak service in the Northeast has also been canceled due to the storm, according to WABC.

Video out of New York City showed ominous clouds rolling in just after 5 p.m. ET.

A tornado watch was issued this afternoon for upstate New York, the Hudson Valley, northeast Pennsylvania, western Connecticut, Massachusetts and southern Vermont. Winds up to 80 mph and large hail are also threats in those areas.

ABC News

Severe storm radar.

The storms will move east quickly this afternoon and are expected to reach the I-95 corridor during the evening rush hour, likely between 5 and 7 p.m.

Philadelphia, New York City and Boston are all under severe thunderstorm watches.

A line of severe t-storms has developed for our west & continues to approach the region. Potential for strong damaging winds, large hail, & isolated tornadoes late this afternoon & this evening. Yellow boxes are severe thunderstorm warnings, red boxes are tornado warnings. pic.twitter.com/8toxH2lfpH